Problem: Luis is 3 times as old as Ishaan and is also 8 years older than Ishaan. How old is Luis?
Answer: We can use the given information to write down two equations that describe the ages of Luis and Ishaan. Let Luis's current age be $l$ and Ishaan's current age be $i$ $l = 3i$ $l = i + 8$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $l$ is to solve the second equation for $i$ and substitute that value into the first equation. Solving our second equation for $i$ , we get: $i = l - 8$ . Substituting this into our first equation, we get the equation: $l = 3$ $(l - 8)$ which combines the information about $l$ from both of our original equations. Simplifying the right side of this equation, we get: $l = 3l - 24$ Solving for $l$ , we get: $2 l = 24$ $l = 12$.